Integrated circuit laser devices are manufactured on wafers which are two inches in diameter and about 12-20 mils thick. After initial manufacture, the wafers are thinned to about 3.5-4.5 mils and separated into smaller units, called sections, with four sections being derived from a single wafer. The sections are trimmed in one dimension, which we will call length, to be about 0.4 inches long. They are also scored across their widths to form 20-30 subdivisions, called bars, which are about 12 mils wide and about 0.4 inches long. During subsequent processing, the sections are divided into bars by breaking or cleaving them along the scribe lines, to form facets along their elongated sides. Each bar is then scribed across its width to form about forty subdivisions, and the bars are cleaved along these score lines to form the individual chips.
Patent application No. 09/004,939, owned by the assignee of the present patent application, discloses a method and apparatus for automated cleaving of laser bars into chips. The bars to be cleaved are sandwiched between two sheets of plastic film in lengthwise, side-by-side arrangement, and are transported between the sheets in a direction perpendicular to the scribe marks defining the sides of the laser chips. At one point, the film sheets with the bars between them pass over a raised breaker assembly. A high pressure air source above the breaker assembly provides a blast of air towards the film sheet enclosed laser bars as they pass over the breaker assembly. This causes the laser bars to fracture or cleave along a scribe line. As the film sheet pass over the breaker assembly, the laser bars are cleaved at each successive scribe line. Thus, downstream of the breaker assembly, there are provided a series of separated chips between the two film sheets.
Although the system of application 09/ achieved an improvement over existing methods of cleaving laser bars and was capable of cleaving several bars simultaneously, it still required the cleaving process to be stopped in order to load each new group of bars to be cleaved.
In accordance with one aspect of a presently preferred embodiment demonstrating objects and features of the present invention, there is provided a method and apparatus for continuous, automated cleaving of a continuous stream of laser bars into chips. The bars to be cleaved are sandwiched between two elongated sheets of plastic film, are arranged in lengthwise alignment along the length of the sheets, and are transported between the sheets in a direction perpendicular to the scribe marks defining the sides of the laser chips, while being supported by a stabilizing surface. At one point, the film sheets with the bars between them pass over a raised breaker assembly on the stabilizing surface. A high pressure air source above the breaker assembly provides a blast of air towards each film sheet enclosed laser bar as it passes over the breaker assembly. This causes the laser bar to fracture or cleave along a scribe line. As the film sheet pass over the breaker assembly, each laser bar is cleaved at each successive scribe line. Thus, downstream of the breaker assembly, there is provided a continuous stream of separated chips between the two film sheets.
One of the reasons for placing the laser bars between the plastic sheets in the system of application No. 09/ was to prevent the bars and separated chips from being blown away by the air stream. However, the air stream causes the top film sheet to vibrate and, in the process, causes the separated chips to imbedded in or adhered to the top sheet.
In accordance with another aspect of a presently preferred embodiment demonstrating objects and features of the present invention, a downwardly projecting air curtain is placed above the top film sheet in close proximity thereto, in order to prevent airflow over the sheet generally parallel to its surface which tends to produce a venturi effect that causes lifting and dropping (vibration) of the sheet.
In accordance with a further aspect of a presently preferred embodiment demonstrating objects and features of the present invention, a sheet of thin, cling-free material, such as onion paper, is provided between one of the sheets of plastic film and the laser bars to prevent adhesion of the bars and separated chips to the plastic film.